They also demand to know why the U.S. mission in Benghazi, Libya, was not better protected and what Secretary of State Hillary Clinton knew before the attacks.

WASHINGTON — Congressional Republicans on Thursday challenged the Obama administration's plan for correcting flaws exposed by the deadly attacks on the U.S. mission in Libya, pressing for an overhaul of its approach to security and probing to discover what Secretary of State Hillary Rodham Clinton and other top officials knew before the attacks.

Three days after an independent investigative panel delivered a stinging report on the department's failures in Benghazi, Libya, GOP lawmakers in open hearings demanded to know why State Department officials had not done more to protect the mission when they were clearly aware that militant attacks on Western targets had been increasing all year.

Republican lawmakers didn't appear to open any unexplored areas for investigation, however. And with a number of GOP lawmakers not showing up for the hearings, it appeared that an issue that has been a major focus of conservatives' efforts since fall may be losing steam.

The Benghazi attacks Sept. 11 killed U.S. Ambassador J. Christopher Stevens and three other Americans and set in motion a broad reexamination of how the State Department protects its 275 posts around the world.

Sen. Bob Corker (R-Tenn.) asked Clinton's deputies, William J. Burns and Thomas R. Nides, why the secretary hadn't sought to shift money to better protect the Benghazi mission, given the stream of violent incidents in the city and warnings from lower-level U.S. officials.

"Why did [Clinton] never ask for … any change of resources to make sure Benghazi was secure? Why did that not happen?" Corker asked at a hearing of the Senate Foreign Relations Committee. "I cannot imagine that we had people out there with the lack of security.... What I saw in the report is a department that has sclerosis."

Administration officials have accepted the conclusion of the investigative panel that security arrangements were deeply flawed, and they have sought to show they are taking the initiative on the issue, which has the potential to affect Clinton's legacy as she prepares to leave office.

State Department officials have embraced all 29 reform proposals recommended by the Accountability Review Board and have removed from their jobs — but not the department — four officials with some responsibility for diplomatic security in Libya. They are asking Congress for more money and reallocating funds to pay for additional Marine guards, civilian security personnel and physical security improvements.

Burns acknowledged that "we did not do a good enough job … in trying to connect the dots" amid signs of mounting danger.

Sen. Marco Rubio (R-Fla.) said the board's report "places a lot of the blame on lower-level officials" and asked how aware Clinton and top aides were of the concerns about the militant threat in Libya.

Burns said there were memos circulating among Clinton and top aides discussing the "deteriorating security situation in Libya." But he said he was not aware of any paper flow to the top level that discussed lower-level officials' requests for greater security funding in Benghazi.

The Republicans rejected arguments by administration officials and their Democratic supporters that part of the problem was the tight budget for diplomatic security, which House Republicans reduced last year. They called instead for a shift of money from lower-priority items.

At an afternoon hearing, the chair of the House Foreign Affairs Committee, Rep. Ileana Ros-Lehtinen (R-Fla.), said the problem was "misplaced priorities." She said the department was "lavishing" money on projects such as a "culinary diplomacy partnership" that sends American chefs around the world, and efforts to slow climate change.

The hearings probably would have drawn more lawmakers if Clinton had testified, as originally planned. But Clinton asked Saturday to be excused because she suffered a concussion in a fall last week. She plans to testify in mid-January, Ros-Lehtinen said.

The State Department said Wednesday night that three officials who had been criticized by the investigative board were giving up their jobs and that Eric Boswell, head of the Diplomatic Security bureau, agreed to resign. The three others were "relieved of their current duties" and have been "placed on administrative leave pending further action," a department statement said.

The statement didn't identify the three, but other officials said they include Charlene Lamb, a deputy assistant secretary in the Diplomatic Security bureau, and Raymond Maxwell, a deputy assistant secretary in the Near Eastern Affairs bureau.